How to extract and copy lines from csv file to another csv file in python?

Question

Let's suppose that I have a big data in a csv file:This is a set of lines from my file:

frame.number    frame.len   frame.cap_len   frame.Type  
  1               100           100           ICMP_tt   
  2                64            64           UDP   
  3               100           100           ICMP_tt   
  4                87            64           ICMP_nn

I want to extract 30 % from this file and put it in another csv file.

I try by using this code but it gives me selection per row not per line:

import csv

data = [] #Buffer list 
with open("E:\\Test.csv", "rb") as the_file:
    reader = csv.reader(the_file, delimiter=",")
    for line in reader:

        try:
            new_line = [line[0], line[1]]
            #Basically ´write the rows to a list
            data.append(new_line)
        except IndexError as e:
            print e
            pass

    with open("E:\\NewTest.csv", "w+") as to_file:
        writer = csv.writer(to_file, delimiter=",")
        for new_line in data:
            writer.writerow(new_line)

I try

metmirr · Accepted Answer · 2017-10-21 23:18:13Z

1

Python csv module use , by default, so its not necessary to specify delimiter unless you have a different delimiter. I suppose you have following csv file:

frame.number,frame.len,frame.cap_len,frame.Type  
1,100,100,ICMP_tt
2,64,64,UDP
3,100,100,ICMP_tt
4,87,64,ICMP_nn

Each line in the file represents a row.

# read
data = []
with open('test.csv', 'r') as f:
    f_csv = csv.reader(f)
    # header = next(f_csv)
    for row in f_csv:
        data.append(row)


# write
with open('newtest.csv', 'w+') as f:
    writer = csv.writer(f)
    for i in range(int(len(data) * 30 / 100)):
        writer.writerow(data[i])

edited Oct 21, 2017 at 23:18

answered Oct 21, 2017 at 23:05

metmirr

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2 Comments

tierrytestu Over a year ago

thank you for you answer but i need to copy only 30% from my file

metmirr Over a year ago

You can stop for loop when you get 30% of file. len(data) * 30 / 100) will give you 30% as line number.

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